The grid-connected photovoltaic installations are formed by a set of photovoltaic modules (photovoltaic generator) and a DC/AC electronic power converter, also referred to as inverter, which conditions the energy produced by the photovoltaic modules and injects it into the power grid.
The inverter converts the direct current (DC) energy generated by the photovoltaic modules to alternating current (AC). Inverters are electronic power converters formed by different elements. Said elements can generally be: a power stage (where direct to alternating current conversion is performed), a filter stage, control devices, sensing elements, power supply sources, protections, monitoring relays, grid-connected relay or contactor and fans, among others.
The state of the art offers different options to feed the different elements forming the converter. One of them consists of feeding the control devices and sensing elements from a DC/DC power supply source which takes energy from the photovoltaic generator. The remaining higher power elements, such as contactors, monitoring relays, fans, etc., are supplied with alternating current (AC) from the power supply grid, because they are generally designed for alternating power supply.
Grid connection regulations for photovoltaic inverters include the need for the inverters to remain connected to the grid during power losses, assuring power supply continuity and therefore system stability.
In inverters with power supply systems where power comes from the AC grid, a power loss causes a power supply loss of the elements and, if the fed elements are contactors, the opening thereof. If it is specifically the grid-connected contactor, the inverter would be disconnected from the grid, not complying with the provisions established in the regulations.
There are different solutions for solving this problem in the state of the art.
The first of them consists of adding to the converter uninterrupted power supply systems that assure supply continuity. However, said systems incorporate batteries that make the system and its maintenance more expensive, while at the same time it is not very robust.
The second solution consists of incorporating capacitor banks, storing energy that will subsequently be used to feed the different elements during the course of the grid fault. The main drawback is that this system must be designed taking into account the maximum power loss time. These times vary in the regulations in force today according to different country requirements, so it would be difficult to design a universal solution. Furthermore, the ratio of energy to occupied volume is low in this solution, so it is necessary to allot a large space for the capacitor banks inside the converter.
Another option consists of replacing the contactors with motor-operated disconnectors. These elements switch from being open to closed and vice versa when a signal is applied to the motor that controls them. If the auxiliary power supply is lost permanently and it is necessary to change state, it will not be possible and the requirements of the regulations that make a disconnection mandatory in response to a power loss or power supply grid fault would not be complied with.
Finally, the literature also contains systems that can be fed in their entirety from the DC side, i.e., from the photovoltaic generator. On one hand, this entails a medium-power DC/DC conversion stage, reducing system efficiency and increasing the final converter cost.
The present invention has a power supply system providing different outputs for different types of loads:                Critical load: load in which the energy supply thereof cannot be lost for correct equipment operation regardless of it being DC or AC, such as the controls, sensors and grid-connected elements such as contactors for example.        Non-critical load: load in which the energy supply thereof can be lost. These are elements that can be temporarily disconnected, such as during a grid fault, for example, because the absence thereof during a short time has no effect on the correct operation of the system. An example of this would be cooling fans, where the increase in the temperature of the system is not altered during a grid fault.        